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</table></div><div></div></div></div></div><div class="t-navbar-sep"> </div><div class="t-navbar-head"><a href="../language.html" title="cpp/language">C++ 语言</a></div><div class="t-navbar-sep"> </div><div class="t-navbar-head"><a href="expressions.html" title="cpp/language/expressions"> 表达式</a><div class="t-navbar-menu"><div><div style="display:inline-block">
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<tr class="t-nv-h2"><td colspan="5"> 概述 </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="value_category.html" title="cpp/language/value category"> 值类别</a>（左值 lvalue、右值 rvalue、亡值 xvalue）</td></tr>
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<tr class="t-nv"><td colspan="5"> <a href="expressions.html#.E5.88.9D.E7.AD.89.E8.A1.A8.E8.BE.BE.E5.BC.8F" title="cpp/language/expressions"> 初等表达式</a></td></tr>
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<tr class="t-nv-h2"><td colspan="5"> 字面量 </td></tr>
<tr class="t-nv"><td colspan="5"> <strong class="selflink">整数字面量</strong></td></tr>
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<tr class="t-nv"><td colspan="5"> <a href="nullptr.html" title="cpp/language/nullptr">空指针字面量</a><span class="t-mark-rev t-since-cxx11">(C++11)</span></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="user_literal.html" title="cpp/language/user literal">用户定义字面量</a><span class="t-mark-rev t-since-cxx11">(C++11)</span></td></tr>
<tr class="t-nv-h2"><td colspan="5"> 运算符 </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="operator_assignment.html" title="cpp/language/operator assignment"> 赋值运算符</a>:
<code>a=b</code>, <code>a+=b</code>, <code>a-=b</code>, <code>a*=b</code>, <code>a/=b</code>, <code>a%=b</code>, <code>a&amp;=b</code>, <code>a|=b</code>, <code>a^=b</code>, <code>a&lt;&lt;=b</code>, <code>a&gt;&gt;=b</code></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="operator_incdec.html" title="cpp/language/operator incdec"> 自增与自减</a>: <code>++a</code>, <code>--a</code>, <code>a++</code>, <code>a--</code></td></tr>
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<code>+a</code>, <code>-a</code>, <code>a+b</code>, <code>a-b</code>, <code>a*b</code>, <code>a/b</code>, <code>a%b</code>, <code>~a</code>, <code>a&amp;b</code>, <code>a|b</code>, <code>a^b</code>, <code>a&lt;&lt;b</code>, <code>a&gt;&gt;b</code> </td></tr>
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<tr class="t-nv"><td colspan="5"> <a href="operator_comparison.html" title="cpp/language/operator comparison"> 比较运算符</a>: <code>a==b</code>, <code>a!=b</code>, <code>a&lt;b</code>, <code>a&gt;b</code>, <code>a&lt;=b</code>, <code>a&gt;=b</code>, <code>a&lt;=&gt;b</code><span class="t-mark-rev t-since-cxx20">(C++20)</span></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="operator_member_access.html" title="cpp/language/operator member access"> 成员访问运算符</a>: <code>a[b]</code>, <code>*a</code>, <code>&amp;a</code>, <code>a-&gt;b</code>, <code>a.b</code>, <code>a-&gt;*b</code>, <code>a.*b</code></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="operator_other.html" title="cpp/language/operator other"> 其他运算符</a>: <code>a(...)</code>, <code>a,b</code>, <code>a?b:c</code> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="default_comparisons.html" title="cpp/language/default comparisons">默认比较</a><span class="t-mark-rev t-since-cxx20">(C++20)</span></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="operator_alternative.html" title="cpp/language/operator alternative">运算符的代用表示</a></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="operator_precedence.html" title="cpp/language/operator precedence">优先级和结合性</a></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="fold.html" title="cpp/language/fold">折叠表达式</a><span class="t-mark-rev t-since-cxx17">(C++17)</span></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="new.html" title="cpp/language/new">new 表达式</a></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="delete.html" title="cpp/language/delete">delete 表达式</a></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="throw.html" title="cpp/language/throw">throw 表达式</a></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="alignof.html" title="cpp/language/alignof">alignof</a></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="sizeof.html" title="cpp/language/sizeof">sizeof</a></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="sizeof....html" title="cpp/language/sizeof...">sizeof...</a><span class="t-mark-rev t-since-cxx11">(C++11)</span></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="typeid.html" title="cpp/language/typeid">typeid</a></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="noexcept.html" title="cpp/language/noexcept">noexcept</a><span class="t-mark-rev t-since-cxx11">(C++11)</span></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="operators.html" title="cpp/language/operators">运算符重载</a></td></tr>
<tr class="t-nv-h2"><td colspan="5"> 类型转换 </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="implicit_cast.html" title="cpp/language/implicit conversion">隐式转换</a></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="const_cast.html" title="cpp/language/const cast">const_cast</a></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="static_cast.html" title="cpp/language/static cast">static_cast</a></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="reinterpret_cast.html" title="cpp/language/reinterpret cast">reinterpret_cast</a></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="dynamic_cast.html" title="cpp/language/dynamic cast">dynamic_cast</a></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="explicit_cast.html" title="cpp/language/explicit cast">显式转换</a> <code>(T)a</code>, <code>T(a)</code></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="cast_operator.html" title="cpp/language/cast operator">用户定义转换</a></td></tr>
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<p>允许在表达式中直接使用整数类型的值。
</p>
<h3><span class="mw-headline" id=".E8.AF.AD.E6.B3.95">语法</span></h3>
<p>整数字面量是下列形式的<a href="expressions.html#.E5.88.9D.E7.AD.89.E8.A1.A8.E8.BE.BE.E5.BC.8F" title="cpp/language/expressions">初等表达式</a>
</p>
<table class="t-sdsc-begin">

<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr>
<tr class="t-sdsc">
<td> <span class="t-spar">十进制字面量</span> <span class="t-spar">整数后缀</span><span class="t-mark">(可选)</span>
</td>
<td> (1)
</td>
<td class="t-sdsc-nopad">
</td></tr>



<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr>
<tr class="t-sdsc">
<td> <span class="t-spar">八进制字面量</span> <span class="t-spar">整数后缀</span><span class="t-mark">(可选)</span>
</td>
<td> (2)
</td>
<td class="t-sdsc-nopad">
</td></tr>



<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr>
<tr class="t-sdsc">
<td> <span class="t-spar">十六进制字面量</span> <span class="t-spar">整数后缀</span><span class="t-mark">(可选)</span>
</td>
<td> (3)
</td>
<td class="t-sdsc-nopad">
</td></tr>



<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr>
<tr class="t-sdsc">
<td> <span class="t-spar">二进制字面量</span> <span class="t-spar">整数后缀</span><span class="t-mark">(可选)</span>
</td>
<td> (4)
</td>
<td> <span class="t-mark-rev t-since-cxx14">(C++14 起)</span>
</td></tr>



<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr></table>
<p>其中
</p>
<ul><li> <span class="t-spar">十进制字面量</span> 是一个非零十进制位（<code>1</code>、<code>2</code>、<code>3</code>、<code>4</code>、<code>5</code>、<code>6</code>、<code>7</code>、<code>8</code>、<code>9</code>）后随零或多个十进制位（<code>0</code>、<code>1</code>、<code>2</code>、<code>3</code>、<code>4</code>、<code>5</code>、<code>6</code>、<code>7</code>、<code>8</code>、<code>9</code>）
</li><li> <span class="t-spar">八进制字面量</span> 是数位零（<code>0</code>）后随零或多个八进制位（<code>0</code>、<code>1</code>、<code>2</code>、<code>3</code>、<code>4</code>、<code>5</code>、<code>6</code>、<code>7</code>）
</li><li> <span class="t-spar">十六进制字面量</span> 是字符序列 <code>0x</code> 或字符序列 <code>0X</code> 后随一或多个十六进制数位（<code>0</code>、<code>1</code>、<code>2</code>、<code>3</code>、<code>4</code>、<code>5</code>、<code>6</code>、<code>7</code>、<code>8</code>、<code>9</code>、<code>a</code>、<code>A</code>、<code>b</code>、<code>B</code>、<code>c</code>、<code>C</code>、<code>d</code>、<code>D</code>、<code>e</code>、<code>E</code>、<code>f</code>、<code>F</code>）
</li><li> <span class="t-spar">二进制字面量</span> 是字符序列 <code>0b</code> 或字符序列 <code>0B</code> 后随一或多个二进制位（<code>0</code>、<code>1</code>）
</li><li> 若提供 <span class="t-spar">整数后缀</span>，则可含有下列一或两者（若均提供，则可以任意顺序出现）：
</li></ul>
<dl><dd><ul><li> <span class="t-spar">无符号后缀</span>（字符 <code>u</code> 或字符 <code>U</code>）
</li><li> <span class="t-spar">长后缀</span>（字符 <code>l</code> 或字符 <code>L</code>）<span class="t-rev-inl t-since-cxx11"><span>或 <span class="t-spar">长长后缀</span>（字符序列 <code>ll</code> 或字符序列 <code>LL</code>）</span> <span><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></span></span>
</li></ul>
</dd></dl>
 <table class="t-rev-begin">
<tr class="t-rev t-since-cxx14"><td>
<p>数位间可插入作为分隔符的可选的单引号（<code>'</code>）。编译器忽略它们。
</p>
</td>
<td><span class="t-mark-rev t-since-cxx14">(C++14 起)</span></td></tr>
</table>
<h3><span class="mw-headline" id=".E8.A7.A3.E9.87.8A">解释</span></h3>
<div class="t-li1"><span class="t-li">1)</span> 十进制整数字面量（以 10 为底，首位为最高位）</div>
<div class="t-li1"><span class="t-li">2)</span> 八进制整数字面量（以 8 为底，首位为最高位）</div>
<div class="t-li1"><span class="t-li">3)</span> 十六进制整数字面量（以 16 为底，首位为最高位，字母 'a' 到 'f' 表示（十进制）值 10 到 15）</div>
<div class="t-li1"><span class="t-li">4)</span> 二进制整数字面量（以 2 为底，首位为最高位）</div>
<p>下列变量被初始化到相同值：
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="cpp source-cpp"><pre class="de1"><span class="kw4">int</span> d <span class="sy1">=</span> <span class="nu0">42</span><span class="sy4">;</span>
<span class="kw4">int</span> o <span class="sy1">=</span> <span class="nu8">052</span><span class="sy4">;</span>
<span class="kw4">int</span> x <span class="sy1">=</span> <span class="nu12">0x2a</span><span class="sy4">;</span>
<span class="kw4">int</span> X <span class="sy1">=</span> <span class="nu12">0X2A</span><span class="sy4">;</span>
<span class="kw4">int</span> b <span class="sy1">=</span> <span class="nu6">0b101010</span><span class="sy4">;</span> <span class="co1">// C++14</span></pre></div></div>
<p>下列变量亦被初始化为相同值：
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="cpp source-cpp"><pre class="de1"><span class="kw4">unsigned</span> <span class="kw4">long</span> <span class="kw4">long</span> l1 <span class="sy1">=</span> 18446744073709550592ull<span class="sy4">;</span> <span class="co1">// C++11</span>
<span class="kw4">unsigned</span> <span class="kw4">long</span> <span class="kw4">long</span> l2 <span class="sy1">=</span> <span class="nu0">18</span><span class="st0">'446'</span><span class="nu0">744</span><span class="st0">'073'</span><span class="nu0">709</span><span class="st0">'550'</span>592llu<span class="sy4">;</span> <span class="co1">// C++14</span>
<span class="kw4">unsigned</span> <span class="kw4">long</span> <span class="kw4">long</span> l3 <span class="sy1">=</span> <span class="nu0">1844</span><span class="st0">'6744'</span><span class="nu8">0737</span><span class="st0">'0955'</span>0592uLL<span class="sy4">;</span> <span class="co1">// C++14</span>
<span class="kw4">unsigned</span> <span class="kw4">long</span> <span class="kw4">long</span> l4 <span class="sy1">=</span> <span class="nu0">184467</span><span class="st0">'440737'</span><span class="nu0">0</span><span class="st0">'95505'</span>92LLU<span class="sy4">;</span> <span class="co1">// C++14</span></pre></div></div>
<h3><span class="mw-headline" id=".E5.AD.97.E9.9D.A2.E9.87.8F.E7.9A.84.E7.B1.BB.E5.9E.8B">字面量的类型</span></h3>
<p>整数字面量的类型，是依赖于所用数字基底和 <span class="t-spar">整数后缀</span> 的列表中，首个能适合其值的类型。
</p>
<table class="wikitable">

<tr style="text-align:center">
<th colspan="3"> 对整数字面量允许的类型
</th></tr>
<tr style="text-align:center">
<td> 后缀
</td>
<td> 十进制底
</td>
<td> 二进制，十六进制或八进制底
</td></tr>
<tr style="text-align:left">
<td> 无后缀
</td>
<td> <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">int</span></span></span>
<p><span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">long</span> <span class="kw4">int</span></span></span><br>
<span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">long</span> <span class="kw4">long</span> <span class="kw4">int</span></span></span><span class="t-mark-rev t-since-cxx11">(C++11 起)</span>
</p>
</td>
<td> <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">int</span></span></span>
<p><span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">unsigned</span> <span class="kw4">int</span></span></span><br>
<span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">long</span> <span class="kw4">int</span></span></span><br>
<span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">unsigned</span> <span class="kw4">long</span> <span class="kw4">int</span></span></span><br>
<span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">long</span> <span class="kw4">long</span> <span class="kw4">int</span></span></span><span class="t-mark-rev t-since-cxx11">(C++11 起)</span><br>
<span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">unsigned</span> <span class="kw4">long</span> <span class="kw4">long</span> <span class="kw4">int</span></span></span><span class="t-mark-rev t-since-cxx11">(C++11 起)</span>
</p>
</td></tr>
<tr>
<td> <code>u</code> 或 <code>U</code>
</td>
<td> <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">unsigned</span> <span class="kw4">int</span></span></span>
<p><span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">unsigned</span> <span class="kw4">long</span> <span class="kw4">int</span></span></span><br>
<span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">unsigned</span> <span class="kw4">long</span> <span class="kw4">long</span> <span class="kw4">int</span></span></span><span class="t-mark-rev t-since-cxx11">(C++11 起)</span>
</p>
</td>
<td> <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">unsigned</span> <span class="kw4">int</span></span></span>
<p><span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">unsigned</span> <span class="kw4">long</span> <span class="kw4">int</span></span></span><br>
<span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">unsigned</span> <span class="kw4">long</span> <span class="kw4">long</span> <span class="kw4">int</span></span></span><span class="t-mark-rev t-since-cxx11">(C++11 起)</span>
</p>
</td></tr>
<tr>
<td> <code>l</code> 或 <code>L</code>
</td>
<td> <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">long</span> <span class="kw4">int</span></span></span>
<p><span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">unsigned</span> <span class="kw4">long</span> <span class="kw4">int</span></span></span><span class="t-mark-rev t-until-cxx11">(C++11 前)</span><br>
<span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">long</span> <span class="kw4">long</span> <span class="kw4">int</span></span></span><span class="t-mark-rev t-since-cxx11">(C++11 起)</span>
</p>
</td>
<td> <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">long</span> <span class="kw4">int</span></span></span>
<p><span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">unsigned</span> <span class="kw4">long</span> <span class="kw4">int</span></span></span><br>
<span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">long</span> <span class="kw4">long</span> <span class="kw4">int</span></span></span><span class="t-mark-rev t-since-cxx11">(C++11 起)</span><br>
<span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">unsigned</span> <span class="kw4">long</span> <span class="kw4">long</span> <span class="kw4">int</span></span></span><span class="t-mark-rev t-since-cxx11">(C++11 起)</span>
</p>
</td></tr>
<tr>
<td> 同时有 <code>l</code>/<code>L</code> 和 <code>u</code>/<code>U</code>
</td>
<td> <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">unsigned</span> <span class="kw4">long</span> <span class="kw4">int</span></span></span>
<p><span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">unsigned</span> <span class="kw4">long</span> <span class="kw4">long</span> <span class="kw4">int</span></span></span><span class="t-mark-rev t-since-cxx11">(C++11 起)</span>
</p>
</td>
<td> <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">unsigned</span> <span class="kw4">long</span> <span class="kw4">int</span></span></span><span class="t-mark-rev t-since-cxx11">(C++11 起)</span>
<p><span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">unsigned</span> <span class="kw4">long</span> <span class="kw4">long</span> <span class="kw4">int</span></span></span><span class="t-mark-rev t-since-cxx11">(C++11 起)</span>
</p>
</td></tr>
<tr>
<td> <code>ll</code> 或 <code>LL</code>
</td>
<td> <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">long</span> <span class="kw4">long</span> <span class="kw4">int</span></span></span><span class="t-mark-rev t-since-cxx11">(C++11 起)</span>
</td>
<td> <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">long</span> <span class="kw4">long</span> <span class="kw4">int</span></span></span><span class="t-mark-rev t-since-cxx11">(C++11 起)</span>
<p><span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">unsigned</span> <span class="kw4">long</span> <span class="kw4">long</span> <span class="kw4">int</span></span></span><span class="t-mark-rev t-since-cxx11">(C++11 起)</span>
</p>
</td></tr>
<tr>
<td> 同时有 <code>ll</code>/<code>LL</code> 和 <code>u</code>/<code>U</code>
</td>
<td> <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">unsigned</span> <span class="kw4">long</span> <span class="kw4">long</span> <span class="kw4">int</span></span></span><span class="t-mark-rev t-since-cxx11">(C++11 起)</span>
</td>
<td> <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">unsigned</span> <span class="kw4">long</span> <span class="kw4">long</span> <span class="kw4">int</span></span></span><span class="t-mark-rev t-since-cxx11">(C++11 起)</span>
</td></tr></table>
<p>若整数字面量的值过大，而无法符合任何后缀/底组合所允许的类型，且编译器支持扩展整数类型（如 <span class="t-c"><span class="mw-geshi cpp source-cpp">__int128</span></span>），则字面量可以被授予扩展整数类型——否则程序非良构。
</p>
<h3><span class="mw-headline" id=".E6.B3.A8.E8.A7.A3">注解</span></h3>
<p>整数字面量中的字母是无关大小写的：<code>0xDeAdBaBeU</code> 与 <code>0XdeadBABEu</code> 表示同一数值（一个例外是 <span class="t-spar">长长后缀</span>，它是 <code>ll</code> 或 <code>LL</code>，而决不能是 <code>lL</code> 或 <code>Ll</code>）
</p><p>没有负整数字面量。如 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">-</span><span class="nu0">1</span></span></span> 这样的表达式对字面量所表示的值运用<a href="operator_arithmetic.html" title="cpp/language/operator arithmetic">一元减运算符</a>，这可能涉及隐式转换。
</p><p>在 C99 之前的 C 中（但不是 C++ 中），不符合 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">long</span> <span class="kw4">int</span></span></span> 的无后缀十进制值允许拥有类型 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">unsigned</span> <span class="kw4">long</span> <span class="kw4">int</span></span></span>。
</p><p>当用于 <a href="../preprocessor/conditional.html" title="cpp/preprocessor/conditional">#if</a> 或 <a href="../../c/preprocessor/conditional.html" title="c/preprocessor/conditional">#elif</a> 的控制表达式时，全部有符号整数常量表现如同它们具有 <span class="t-lc"><a href="../types/integer.html" title="cpp/types/integer">std::intmax_t</a></span> 类型，而全部无符号整数常量表现如同它们具有 <span class="t-lc"><a href="../types/integer.html" title="cpp/types/integer">std::uintmax_t</a></span> 类型。
</p><p>由于<a href="translation_phases.html#.E6.9C.80.E5.A4.A7.E5.90.9E.E5.99.AC" title="cpp/language/translation phases">最大吞噬</a>规则，以 <code>e</code> 和 <code>E</code> 结束的十六进制整数字面量在后随运算符 <code>+</code> 或 <code>-</code> 时，源码中必须以空白符或括号将它们与运算符分隔：
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="cpp source-cpp"><pre class="de1"><span class="kw4">auto</span> x <span class="sy1">=</span> <span class="nu12">0xE</span><span class="sy2">+</span><span class="nu16">2.0</span><span class="sy4">;</span>   <span class="co1">// 错误</span>
<span class="kw4">auto</span> y <span class="sy1">=</span> <span class="nu12">0xa</span><span class="sy2">+</span><span class="nu16">2.0</span><span class="sy4">;</span>   <span class="co1">// OK</span>
<span class="kw4">auto</span> z <span class="sy1">=</span> <span class="nu12">0xE</span> <span class="sy2">+</span><span class="nu16">2.0</span><span class="sy4">;</span>  <span class="co1">// OK</span>
<span class="kw4">auto</span> q <span class="sy1">=</span> <span class="br0">(</span><span class="nu12">0xE</span><span class="br0">)</span><span class="sy2">+</span><span class="nu16">2.0</span><span class="sy4">;</span> <span class="co1">// OK</span></pre></div></div>
<p>否则，将构成一个非法的预处理数字记号，并导致进一步的分析失败。
</p>
<h3><span class="mw-headline" id=".E7.A4.BA.E4.BE.8B">示例</span></h3>
<div class="t-example"><div class="t-example-live-link"><div class="coliru-btn coliru-btn-run-init">运行此代码</div></div>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="cpp source-cpp"><pre class="de1"><span class="co2">#include &lt;iostream&gt;</span>
 
<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span>
<span class="br0">{</span>
<a href="../io/cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> <span class="nu0">123</span>    <span class="sy1">&lt;&lt;</span> <span class="st0">'<span class="es1">\n</span>'</span>
          <span class="sy1">&lt;&lt;</span> <span class="nu8">0123</span>   <span class="sy1">&lt;&lt;</span> <span class="st0">'<span class="es1">\n</span>'</span>
          <span class="sy1">&lt;&lt;</span> <span class="nu12">0x123</span>  <span class="sy1">&lt;&lt;</span> <span class="st0">'<span class="es1">\n</span>'</span>
          <span class="sy1">&lt;&lt;</span> <span class="nu6">0b10</span>   <span class="sy1">&lt;&lt;</span> <span class="st0">'<span class="es1">\n</span>'</span>
          <span class="sy1">&lt;&lt;</span> 12345678901234567890ull <span class="sy1">&lt;&lt;</span> <span class="st0">'<span class="es1">\n</span>'</span>
          <span class="sy1">&lt;&lt;</span> 12345678901234567890u   <span class="sy1">&lt;&lt;</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span> <span class="co1">// 类型是 unsigned long long</span>
                                              <span class="co1">// 即使无 long long 后缀</span>
 
<span class="co1">//   std::cout &lt;&lt; -9223372036854775808 &lt;&lt; '\n'; // 错误：值 9223372036854775808</span>
                <span class="co1">// 不吻合 signed long long，这是无后缀整数字面量允许的最大类型</span>
     <a href="../io/cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> <span class="sy2">-</span>9223372036854775808u <span class="sy1">&lt;&lt;</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span> <span class="co1">// 应用于无符号值的一元减</span>
                <span class="co1">// 从 2^64 减去该值，给出 9223372036854775808</span>
     <a href="../io/cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> <span class="sy2">-</span><span class="nu0">9223372036854775807</span> <span class="sy2">-</span> <span class="nu0">1</span> <span class="sy1">&lt;&lt;</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span> <span class="co1">// 计算值 -9223372036854775808</span>
                                                    <span class="co1">// 的正确方式</span>
<span class="br0">}</span></pre></div></div>
<p>输出：
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="text source-text"><pre class="de1">123
83
291
2
12345678901234567890
12345678901234567890
9223372036854775808
-9223372036854775808</pre></div></div> 
</div>
<h3><span class="mw-headline" id=".E5.8F.82.E9.98.85">参阅</span></h3>
<table class="t-dsc-begin">

<tr class="t-dsc">
<td>  <a href="user_literal.html" title="cpp/language/user literal">用户定义字面量</a>
</td>
<td>  拥有用户定义后缀的字面量<span class="t-mark-rev t-since-cxx11">(C++11)</span> </td></tr>

</table>

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